Absence of interaction between ferroelectric and incommensurate transitions in Ba2NaNb5(1-x)Ta5xO15

Features of both the ferroelectric and incommensurate transitions in ${\mathrm{Ba}}_{2}$${\mathrm{NaNb}}_{5(1\mathrm{\ensuremath{-}}\mathit{x})}$${\mathrm{Ta}}_{5\mathit{x}}$${\mathrm{O}}_{15}$ were investigated by means of a transmission electron microscope in order to find the relationship between these transitions. An in situ observation of the transitions revealed that the ferroelectric transition takes place around 373 K in x=0.57 while the incommensurate transition occurs around 543 K. Because the ferroelectric transition does not basically accompany a change in microstructures related to the incommensurate lattice modulation, there is no interaction between these two transitions.